1. Field of the Invention
The present invention relates to an electric power steering apparatus for assisting the force required to turn the steering wheel of a vehicle.
2. Description of the Related Art
An electric power steering apparatus for a vehicle uses an electric motor to assist the steering force required to steer the vehicle. The electric power steering apparatus includes a steering mechanism which is linked via a shaft a steering wheel and which is provided with a non-contact torque sensor for detecting the rotational force applied at the steering wheel, as well as the electric motor for assisting the operation of the steering mechanism; the electric motor is driven in response to the torque detected by the torque sensor to lessen the steering force at the steering wheel.
The torque sensor has the construction shown, for example, in FIG. 1, FIG. 1 is a cross sectional view of a torque sensor used in a conventional electric power steering apparatus, The reference numeral 1a designates an input shaft connected to a steering wheel (not shown), and the input shaft 1a is concentrically connected through a torsion. bar 1c to an output shaft 1b connected to a steering mechanism (not shown). At the connection between the input shaft 1a and the output shaft 1b, there is mounted a non-contact torque sensor 2 which contains in its housing 21 a magnetic coupler 22 whose magnetic coupling changes in accordance with the twisting of the torsion bar 1c. The torque sensor 2 detects the change in the magnetic coupling and performs predetermined signal processing on tile detected change to measure the steering torque applied to the torsion bar 1c. A signal processing circuit (not shown) formed on a torque sensor circuit board 23 disposed outwardly of the magnetic coupler 22 within the housing 21 is used for the signal processing.
The result of ,he signal processing by the signal processing circuit (the torque detection signal) is inputted to a control circuit 30 formed on a control circuit board (not shown) disposed at a preset place outside the torque sensor 2. The control circuit 30 controls the driving of the electric motor according to the steering torque measured by the torque sensor 2.
However, in the above conventional electric power steering apparatus, since the torque sensor circuit board 23 and the control circuit board are disposed at respectively separate places, the number of components and the manhour required for the production of the apparatus increase accordingly, resulting in an increase in the production cost of the apparatus.